The invention relates to corrosion prevention in water systems. In particular, it relates to the use of a chemical additive in the water of a cooling water system to prevent corrosion and scale deposits on metal surfaces in such a circulating water system.
In present methods of controlling corrosion and scale in water systems, additives, usually in very small proportions, to the circulating water commonly are used. Additives containing metal compounds, particularly chromates, are offered commercially for these purposes. Such metal compounds have the disadvantage of toxicity; and, they pose a water pollution problem if they are discharged into a natural watercourse. While some non-toxic, biodegradable organic additives have been proposed, their inhibiting effects have usually been less than satisfactory. U.S. Pat. No. 2,529,177 proposed the addition of certain hydroxy-polycarboxylic acids such as citric, malic, tartaric and mucic acids, or their soluble salts, to water systems for control of corrosion and tuberculation in water pipes. That patent suggested that hydroxy-polycarboxylic acids would be attracted from the water solution to metal surfaces in the system and would form a protective organic layer on the metal surfaces. Although these additives have the advantages of non-toxicity and biodegradability, they have not been effective for practical control of corrosion and scale, in most instances.
The present invention provides organic compound additives for cooling water in a circulating water system, which are effective as inhibitors of scale and corrosion when added in very small proportions. These additives have the advantage of non-toxicity and biodegradability and are found to be effective for practical control of corrosion and scale in open cooling water systems, under most ordinary operating conditions.
Additives found useful in accordance with the invention belong to a class of organic compounds having a combination of several functional groups in the organic molecule. Each of these groups incorporated in the molecule is necessary or advantageous for the effective corrosion and scale inhibiting function of the additive.
The compound includes an organic sulfonate, an organic phosphonate or an organic carboxylate group, which provides an anchoring functional group in the molecule, by which the molecule is attracted to the metal surfaces in the system. This anchoring effect is similar to that performed by the carboxyl radical in the hydroxy-polycarboxylate additives that were described in U.S. Pat. No. 2,529,177.
The molecule of an additive compound of the present invention additionally includes an oleophilic terminal hydrocarbon chain which, in itself, enhances the inhibiting function of the additive. When used in combination with an oil additive in the circulating water, it functions further to improve the corrosion and scale inhibiting effects. This oleophilic terminal group serves to attract dispersed oil from the circulating water, and binds it in the protective film which is formed by the additive compound on the metallic surfaces of the system. Accordingly, when a minor amount of the additive is dissolved in the circulating water, the additive will be anchored or adsorbed on metal surfaces through the action of the anchoring functional group so as to form an effective protective film on such surfaces. When a minor proportion of an oil or a substituted hydrocarbon also is dispersed into the circulating water, the oleophilic functional group of the additive compound will attract the dispersed hydrocarbon to the protective film to even further enhance the protective function of the film on the metallic surfaces.
The inclusion of a terminal hydrocarbon chain on the molecule as an oleophilic functional group will tend to insolubilize the compound. Since solubility of the compound in water is important for the proper functioning of the additive, the compound developed by this invention further includes a solubilizing functional group in addition to the other functional groups described above.